The Wolff rearrangement is a rearrangement reaction converting a α-diazo-ketone into a ketene. This reaction was first reported by Ludwig Wolff in 1902.
The rearrangement is catalyzed by light, heat, or a transition metal catalyst such as silver oxide. Nitrogen gas is expelled forming a carbenic intermediate which rearranges. This 1,2-rearrangement is the key step in the Arndt-Eistert synthesis.
The reaction may or may not proceed in a concerted mechanism. A carbene intermediate is avoided if the reaction proceeds through the concerted mechanism. Mechanistic studies have been aimed at determining if migration is concerted with loss of nitrogen. The conclusion that has emerged is that a carbene is generated in photochemical reactions but the reaction can be concerted under the thermal conditions.
In one application, the Wolff rearrangement is performed in an electrochemical setup in which the catalyst silver oxide is reduced to elemental silver in the shape of monodisperse nanoparticles (2-4 nm diameter) which trigger the decomposition of the diazoketone by the formation of a radical cation.